The present application relates to thickening water-in-oil lattices, to a process for their preparation and to their application as thickeners and/or emulsifiers for skincare products and haircare products or for the manufacture of cosmetic, dermo-pharmaceutical or pharmaceutical preparations.
Various thickeners exist and are already used for these purposes. Natural products such as guar gum or corn starch are known in particular, the drawbacks of which are those inherent to natural products, such as price fluctuations, supply difficulties and random quality.
Synthetic polymers in powder form, mainly polyacrylic acids, are also widely used but have the drawback of requiring neutralization when they are used, since they only develop their viscosity from a pH  greater than 6.5 and they are often difficult to dissolve.
Synthetic thickening polymers in the form of an inverted latex, that is to say one in which the continuous phase is an oil, are also known. These latlices dissolve extremely quickly; the polymers contained in these inverted lattices are usually acrylamide/alkali metal acrylate copolymers or acrylamide/sodium 2-acrylamido-2-methylpropane-sulphonate copolymers; they are already neutralized and when they are dissolved in water, for example to a concentration of 1%, it is observed that the pH is generally above 6.
However, acrylamide/sodium acrylate copolymers do not develop any appreciable thickening properties when the pH is lowered below 6; on the other hand, the acrylamide/sodium 2-acrylamido-2-methylpropane-sulphonate copolymers described in EP 0,503,853 retain an appreciable thickening capacity even at pH 4.
However, such copolymers have monoacrylamide contents which, although extremely low, could result in making them impossible to use in cosmetics in the near future, following changes in the European legislation on hazardous substances.
The Applicant has thus been concerned with the synthesis and development of polymers that thicken, even at acidic pH, in the form of an inverted latex, without using monoacrylamide.
The subject of the invention is a process for the preparation of a composition comprising an oil phase, an aqueous phase, at least one emulsifier of water-in-oil (W/O) type, at least one emulsifier of oil-in-water (O/W) type, characterized in that the said composition is an inverted latex comprising from 20% to 70% by weight, and preferably from 25% to 45% by weight, of a branched or crosslinked anionic polyelectrolyte based on a monomer possessing a strongly acidic function, characterized in that:
a) an aqueous solution containing the monomers and the optional additives is emulsified in an oil phase in the presence of one or more emulsifiers of water-in-oil type,
b) the polymerization reaction is initiated by introducing a free-radical initiator into the emulsion formed in a), after which the reaction is left to proceed,
c) when the polymerization reaction is complete, one or more emulsifiers of oil-in-water type are introduced at a temperature below 50xc2x0 C.
The expression xe2x80x9cemulsifier of the water-in-oil typexe2x80x9d is understood to denote emulsifiers having an HLB value that is low enough to give water-in-oil emulsions, such as the surfactant polymers sold under the name Hypermer(trademark) or such as sorbitan extracts, for instance sorbitan monooleate sold by the company SEPPIC under the tradename Montane 80(trademark), or sorbitan isostearate sold by SEPPIC under the name Montane 70(trademark).
The expression xe2x80x9cemulsifier of the oil-in-water typexe2x80x9d is understood to denote emulsifiers having an HLB value that is high enough to give oil-in-water emulsions, such as ethoxylated sorbitan esters, for instance sorbitan oleate ethoxylated with 20 mol of ethylene oxide, castor oil ethoxylated with 40 mol of ethylene oxide, sorbitan laurate ethoxylated with 20 mol of ethylene oxide or lauryl alcohol ethoxylated with 7 mol of ethylene oxide.
The term branched polymer is understood to denote a non-linear polymer which has pendant chains so as to obtain, when this polymer is dissolved in water, a high degree of entangling leading to very high low-gradient viscosities.
The term crosslinked polymer is understood to denote a non-linear polymer in the form of a three-dimensional network which is insoluble in water but swellable in water and thus leading to the production of a chemical gel.
The composition prepared by the process according to the invention can contain crosslinked units and/or branched units.
The subject of the invention is, in particular, a process as defined above, characterized in that the polymerization of its precursor monomers is carried out at a pH below 4, and more particularly below or equal to 3.5.
The strongly acidic function of the monomer containing it is, in particular, a sulphonic acid function or a phosphonic acid function, which are partially or totally salified, and the said monomer is preferably chosen from2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulphonic acid which is partially or totally salified in the form of the sodium salt or the ammonium salt.
The subject of the invention is, more particularly, a process as defined above, characterized in that the anionic polyelectrolyte is crosslinked and/or branched with a diethylenic or polyethylenic compound in molar proportion, expressed relative to the monomers used, of from 0.005% to 1% and preferably from 0.01% to 0.1%, and preferably that for which the crosslinking agent and/or the branching agent is chosen from ethylene glycol methacrylate, sodium diallyloxyacetate, diethylene glycol diacrylate, diallylurea, trimethylolpropane triacrylate or methylenebisacrylamide.
The latex according to the invention generally contains from 2.5% to 15% by weight, and preferably from 4% to 9% by weight, of emulsifiers, among which from 20% to 50%, in particular from 25% to 40%, of the total weight of the emulsifiers present are of the water-in-oil (W/O) type and in which from 80% to 50%, in particular from 75% to 60%, of the total weight of the emulsifiers are of the oil-in-water (O/W) type. Such latices also form the subject of the present invention.
According to a specific aspect, the composition as defined above is characterized in that the oil phase represents from 15% to 40%, preferably from 20% to 25%, of its total weight.
This oil phase either consists of a commercial mineral oil containing saturated hydrocarbons such as paraffins, isoparaffins or cycloparaffins, having, at room temperature, a density of between 0.7 and 0.9 and a boiling point above 180xc2x0 C., such as, for example, Exxol(trademark) D 100 S or Marcol(trademark) 52 sold by Exxon Chemical, isohexadecane or isododecane sold by Bayer, or consists of a plant oil or a synthetic oil or of a mixture of several of these oils.
According to a preferred aspect of the present invention, the oil phase consists of Marcol(trademark) 52 or of isohexadecane; isohexadecane, which is identified in Chemical Abstracts by the number RN=93685-80-4, is a mixture of C12, C16 and C20 isoparaffins containing at least 97% of C16 isoparaffins, among which the main constituent is 2,2,4,4,6,8,8-heptamethylnonane (RN=4390-04-9). It is marketed in France by the company Bayer. Marcol(trademark) 52 is a commercial oil corresponding to the definition of liquid petroleum jellies in the French Codex. This is a white mineral oil in accordance with the FDA Regulations 21 CFR 172.878 and CFR 178.3620 (a) and it is listed in the USA Pharmacopoeia, US XXIII (1995) and in the European Pharmacopoeia (1993).
The latices contain between 20% and 50% water. The latices according to the invention can also contain various additives such as complexing agents, transfer agents or chain-limiting agents.
According to another aspect of the present invention, its subject is a process for preparing the composition as defined above, characterized in that:
a) an aqueous solution containing the monomers and the optional additives is emulsified in an oil phase in the presence of one or more emulsifiers of water-in-oil type,
b) the polymerization reaction is initiated by introducing a free-radical initiator into the emulsion formed in a), after which the reaction is left to proceed,
c) when the polymerization reaction is complete, one or more emulsifiers of oil-in-water type are introduced at a temperature below 50xc2x0 C.
According to a variant of this process, the reaction medium obtained after step b) is concentrated by distillation before step c) is carried out.
According to a preferred variant of the process as defined above, the polymerization reaction is initiated by a redox couple, which may be of organic or inorganic nature, such as the cumene hydroperoxide/sodium metabisulphite couple or the cumene hydroperoxide/thionyl chloride (SOCl2) couple, at a temperature below or equal to 10xc2x0 C., and is then carried out either in a virtually adiabatic manner up to a temperature above or equal to 40xc2x0 C., and more particularly above or equal to 50xc2x0 C., or by controlling the temperature profile. According to another variant of the process as defined above, the polymerization reaction is carried out at constant temperature. In this case, it is advantageous to use azobis(iso-butyronitrile) (AIBN) between 40xc2x0 C. and 45xc2x0 C.
According to another preferred embodiment of the process, the starting aqueous solution is adjusted to a pH below or equal to 3.5.
The subject of the invention is also the use of the composition as defined above for preparing a cosmetic, dermo-pharmaceutical or pharmaceutical topical composition.
A topical composition according to the invention, intended to be applied to the skin or mucous membranes of humans or animals can consist of a topical emulsion comprising at least one aqueous phase and at least one oil phase. This topical emulsion can be of the oil-in-water type. More particularly, this topical emulsion can consist of a fluid emulsion, such as a fluid gel or milk. The oil phase of the topical emulsion can consist of a mixture of one or more oils.
A topical composition according to the invention can be intended for cosmetic use or can be used to prepare a medical product intended for the treatment of mucous and skin diseases. In the latter case, the topical composition then contains an active principle which can consist, for example, of an anti-inflammatory agent, a muscle relaxant, an antifungal agent or an antibacterial agent.
When the topical composition is used as a cosmetic composition intended to be applied to the skin or mucous membranes, it may or may not contain an active principle, for example a moisturizer, a tanning agent, a sunscreen, an anti-wrinkle agent, a slimming agent, an anti-radical agent, an antiacne agent or an antifungal agent.
A topical composition according to the invention usually contains between 0.1% and 10% by weight of the thickener defined above. The pH of the topical composition is preferably above or equal to 5, more preferably between 6 and 12.
The topical composition can also contain compounds conventionally included in compositions of this type, for example fragrances, preserving agents, dyes, emollients or surfactants.
According to yet another aspect, the invention relates to the use of the novel thickener mentioned above, in accordance with the invention, to thicken and emulsify a topical composition comprising at least one aqueous phase.
The composition according to the invention is an advantageous substitute for those sold under the name Sepigel(trademark) 305 or Sepigel(trademark) 501 by the Applicant, since it also has good compatibility with the other excipients used for the preparation of formulations such as milks, lotions, creams, soaps, baths, balms, shampoos or conditioners.
In particular, the composition is compatible with the concentrates described and claimed in the international publications WO 92/06778, WO 95/04592, WO 95/13863, WO 96/37285, WO 98/22207, WO 98/47610 or FR 2,734,496, and with the surfactants described in WO 93/08204.
The composition is particularly compatible with Montanov(copyright) 68, Montanov(trademark) 82, Montanov(trademark) 202 or Sepiperl(trademark) N. It can also be used in emulsions of the type described and claimed in EP 0,629,396 and in cosmetically or physiologically acceptable aqueous dispersions with an organopolysiloxane compound chosen, for example, from those described in WO 93/05762 or in WO 93/21316.
The composition can also be used to form cosmetically or physiologically acceptable gels that are aqueous at acidic pH, such as those described in WO 93/07856; it can also be used in combination with nonionic celluloses in order to form, for example, styling gels, such as those described in EP 0,684,024, or alternatively in combination with fatty acid esters of a sugar, in order to form compositions for treating the hair or the skin, such as those described in EP 0,603,019, or alternatively in shampoos or conditioners as described and claimed in WO 92/21316, or, lastly, in combination with an anionic homopolymer such as Carbopol(trademark) in order to form hair-treatment products, such as those described in DE 195 23596.
The composition according to the invention is also compatible with active principles such as, for example, self-tanning agents, for instance dihydroxyacetone (DHA) or antiacne agents, and it can thus be introduced into self-tanning compositions such as those claimed in EP 0,715,845, EP 0,604,249, EP 0,576,188 or in WO 93/07902.
The composition is also compatible with N-acylated derivatives of amino acids, which allows it to be used in soothing compositions especially for sensitive skin, such as those described or claimed in WO 92/21318, WO 94/27561, WO 98/09611 or WO 99/00109.